Hey guys,

I'm going to be making my own templates, and I was just wondering how far the standard RB or Mazdatrix templates open up the top of the ports. I just want a mild/ medium port job.

Thanks, Matt

 

RB Street Port - The templates are shown here. For a mild street performance improvement, without screwing up the driveability, you might want to consider the scheme I have been using on my most recent motors. I do the RB intake porting on the ports that are fed by the secondaries (the larger throats in the carb). For the primary ports I just do a cleanup, with very little change in the timing. For the exhaust, I port it out to match the outlet side of the housing, somewhat less radical than the RB template. This gives driveability just like a stock motor, and you get most of the benefit at full throttle from the secondaries. My current driver has a 12a with this porting, a RB header with stock muffler and an RX-4 carb with a custom intake manifold. It dynoed 130 HP to the wheels.

All the experts, including RB, say that if you are only going to do one thing to improve performance, install a header. This tells me that the exhaust ports are NOT the limiting factor for performance. Once you install a header, it becomes very difficult to quiet down these motors. The bigger you make the exhaust port, the louder it will be. Unless you are planning to race it, the main effect of bigger exhaust ports is more noise.

 

thats very helpful, thanks. But does anybody actually know or could measure how much larger in mm the streetport extendeds the top of the stock port?

Thanks, Matt

 

Have you looked over on the porting sub forum on nopistons?

Stillettoman, I see your doing the exhaust opening with a curve to bring on the flow more controlled. I just read about that over on that other forum. Interesting concept. Any thoughts on its performance versus a straight line?

 

Carl -

My only experience with a "straight line" exhaust porting was with a set of brand new housings someone gave me, that had been ported with square exhaust ports. That is ridiculous, but they were free so I built an engine. It idled like a street rod with a lumpy cam, but the main effect was that it was ungodly loud, and nothing would quiet it. Surprisingly, the gas mileage and driveability were not bad.

Incidentally, the photo I showed above is the RB street port template. What I described, and what I have been using is much less radical, but rounded slightly on the bottom side.